pruning viburnum davidii

I planted 3 viburnum davidii shrubs in a group about 8 years ago and they've been very healthy and looked nice. Just recently when I was checking my shrubs I noticed they were all covered in black spot s - similar to the disease you get on rose bushes. I've chopped them all down to stumps about 6 inches high as they were so unsightly (I've got my garden open to the public next month) Have I been too extreme? Will they grow back or shall I dig up the stumps and put in something else? In the meantime I've planted loads of cosmos and other tall annuals to disguise the devastation. Advice needed please.